Usher Syndrome, a rare genetic disorder and a leading cause of deafness and blindness, is associated with a mutation in any one of ten genes. Other names for the syndrome include Hallgren Syndrome, Usher-Hallgren Syndrome, RP-Dysacusis Syndrome, and Dystrophia Retinae Dysacusis Syndrome.
Usher Syndrome is characterized by deafness and gradual vision loss. The hearing loss is associated with inner ear defects, whereas the vision loss is associated with retinitis pigmentosa (RP), a degeneration of the retinal cells. Usually, the rod cells of the retina are affected first, leading to early night blindness and the gradual loss of peripheral vision. Some cases involve early degeneration of the cone cells of the macula, leading to a loss of central acuity. In some cases, the sufferer's foveal vision is spared, leading to “doughnut vision,” in which central and peripheral vision remain intact, but interrupted by a ring of blindness.
Usher Syndrome has three clinical subtypes, denoted: I, II and III. Usher I subjects are born profoundly deaf, begin to lose vision within ten years and exhibit balance difficulties. They are slow to learn to walk as children, due to vestibular abnormalities. Usher II subjects suffer lesser hearing loss, do not suffer physical imbalance and begin to lose vision in adolescence. Much of their hearing can be preserved into middle age. Usher III subjects suffer gradual loss of hearing and vision and can suffer physical imbalance.
Usher Syndrome is a variable condition; the degree of severity is not tightly linked to subtype. For example, an Usher III subject might be asymptomatic in childhood, but develop profound hearing and vision loss by early to mid adulthood. Substantial visual impairment prior to age 50 is common in Usher III subjects. An Usher I subject, on the other hand, might be deaf from birth, but sustain good central vision into old age.